Obama pledged in his inaugural speech Monday to respond to what he called the threat of climate change, saying: "Failure to do so would betray our children and future generations."
By singling out climate change, Obama indicated a willingness to take on an issue that he acknowledges was often overlooked during his first term. He also was setting up a likely confrontation with congressional Republicans who have opposed legislative efforts to curb global warming.
Environmental groups said the president's first test on climate change could come early this year as he decides whether to approve the Keystone XL oil pipeline that will carry tar sands oil from Alberta, Canada, to Texas.
The State Department is reviewing the pipeline and is expected to make a recommendation to Obama as soon as April. The State Department has federal jurisdiction because the $7 billion pipeline begins in Canada.
Obama blocked the pipeline last year, citing uncertainty over the project's route through environmentally sensitive land in Nebraska. On Tuesday, the state's Republican governor, Dave Heineman, gave his approval to a revised route for the pipeline, a widely anticipated move that nonetheless added to the political pressure for the Obama administration to
Republicans and many business groups say the project would help achieve energy independence for North America and create thousands of jobs.
But environmental groups say the pipeline would transport "dirty oil" and produce heat-trapping gases that contribute to global warming. They also worry about a possible spill.
"Starting with rejecting the Keystone XL pipeline, the president must make fighting global warming a central priority," said Margie Alt, executive director of Environment America.
Sen. Barbara Boxer, D-Calif., chairwoman of the Senate Environment and Public Works Committee, called Obama's comments on climate change "exactly right."
Andrew Hoffman, director of the Erb Institute for Global Sustainable Enterprise at the University of Michigan, said Obama's focus on climate showed political backbone.
"He finally had the courage to acknowledge the words 'climate change,'" Hoffman said, adding that Obama and other administration officials have frequently used words such as green jobs or clean energy to describe energy policy, instead of the more politically charged term.
"I find it very interesting that in this second term he's just coming right out and saying that climate change is exactly what we're dealing with," Hoffman said.
But on Tuesday, the first full day of Obama's second term, the White House disputed the notion that the president had waited until his second term to tackle climate issues, pointing to first-term accomplishments such as improved fuel-economy standards for cars and trucks.
White House spokesman Jay Carney called climate change "an important issue" and a priority for the president. "But it is not a singular priority. It is one of a host of priorities he believes we can act on," Carney said.
State Department spokeswoman Victoria Nuland said the department would study a three-page letter from Heineman and Nebraska's environmental report as it completes its own review of the pipeline. A decision is not expected before the end of March, Nuland said Tuesday.
Obama, in his address, said some people "may still deny the overwhelming judgment of science" that global warming exists and has human causes, "but none can avoid the devastating impact of raging fires and crippling drought and more powerful storms."
The president has pledged to boost renewable energy sources such as wind and solar power, along with more traditional energy sources such as coal, oil and natural gas.
"The path toward sustainable energy sources will be long and sometimes difficult. But America cannot resist this transition. We must lead it," Obama said.
He said developing new energy technologies will lead to jobs and new industries. "That is how we will preserve our planet," he said.
Alden Meyer, director of strategy and policy at the Union of Concerned Scientists, said Obama's "clarion call to action" on climate change "leaves no doubt this will be a priority in his second term."
After Hurricane Sandy and other extreme weather events, there has been more political momentum than ever to address climate change, Meyer said.
"With presidential leadership, that shift will continue and deepen over the next four years, and meaningful progress on climate change will become an important part of Barack Obama's legacy as president," he said.
Alt and other environmental leaders said they are counting on Obama to set tough limits on carbon pollution from coal-fired power plants and to continue federal investments in renewable energy sources such as wind and solar power.
Obama tried and failed in his first term to get a climate change bill through Congress. Some Democratic lawmakers and environmentalists have pushed for a tax on carbon pollution, but White House officials say they have no plan to propose one.
Scott Segal, an energy lobbyist who represents utilities and natural gas drillers, said Obama "missed the opportunity to remind listeners that climate change is an international phenomenon" that will require international solutions.
By imposing "inflexible" national policies to curb climate change, Obama could restrain the U.S. economy without delivering promised solutions, Segal said.
Associated Press writers Josh Lederman and Bradley Klapper contributed to this report.
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